Post-maximum high-resolution spectroscopy of SN2014J in M82

ATel #5965; H. Meusinger (TLS Tautenburg), H. Lehmann (TLS Tautenburg)
on 10 Mar 2014; 09:44 UT
Credential Certification: Helmut Meusinger (meus@tls-tautenburg.de)

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We obtained an optical high-resolution spectrum of SN2014J with the Coude echelle spectrograph attached to the 2-m Alfred Jensch Telescope of the Thüringer Landessternwarte Tautenburg on Feb. 12.0 (mean JD 2456700.47). Six 2400s spectra of the supernova were taken, together with spectra of the spectrophotometric standard star BD+75325. The six spectra were separately reduced, flux calibrated, and co-added because no radial velocity variations in the absorption features were found. The final spectrum covers the wavelength range 4430 Å to 7030 Å with a resolving power of 32000 and a signal-to-noise ratio of 115. We de-reddened the spectrum with the Milky Way extinction curve and searched for best matches within the database of 2603 SN Ia spectra from Blondin et al. (2012, AJ 142, 126) adopting E(B-V) = 0.14 for the reddening in our Galaxy and an additional E(B-V) for the M82 dust as a free parameter. Good agreement was found for several SNe of the Branch class BL and the Wang class HV at 10±1 days after maximum light: 1997do (0.9-1.0), 2001bg (0.8-1.0), 2006cp (0.9), and 2007le (0.7-0.9), where the values in parenthesis are the best matching values of E(B-V) for the reddening in M82. Adopting E(B-V) = 0.40 from Phillips et al. (2013; ApJ 779, 38) for SN 2007le, we estimate E(B-V)_host = 1.1 for the reddening of SN 2014J in its host galaxy, consistent with previous estimates (Goobar et al. 2014, arXiv:1402.0849v2). The post-maximum expansion velocity measured from the SiII (6355A) line is v(SiII)≈11400 km/s. The comparison with the data given by Goobar et al. (2014; Fig. 3) yields a steep velocity gradient dv/dt ≈ 90 km/s/day. The Na I D doublet remains very strong, with a variety of M82 absorption features covering velocities from about +40 to +300 km/s, and is saturated between 73 km/s and 120/135 km/s for Na I 5895.9Å/5889.9Å. The fine structure of the doublet is highly similar to that seen in the pre-maximum spectrum shown by Goobar et al. (2014; Fig. 4). We also confirm the diffuse interstellar bands (DIBs) in M82 reported by Ritchey et al. (ATEL #5859), though those bluewards of the 5487.7Å DIB are only tentatively detected. The velocity of the DIBs 4963.9Å, 5487.7Å, 5780.5Å, 5797.1Å, 6283.8Å, and 6613.6Å is about +125 km/s, coincident with the centers of the Na I D lines. The measured equivalent widths are 397±109 mÅ (5780.5Å), 311±39 mÅ (5797.1Å), 375±21 mÅ (6196.0Å), and 215±30 mÅ (6613.6Å). According to the empirical relation from Phillips et al. (2013), the EW of 5780.5Å corresponds to a visual extinction A_v_host = 2.1±0.5 mag and therewith to a low ratio of total-to-selective extinction R_v_host = 2.1±0.5, in agreement with ATEL #5830. More detailed modeling is necessary to reduce the large EW errors which are dominated by the uncertainty in the exact choice of the continuum.